text:
Why don't aircraft fly over Tibet?
If you open www.flightradar24.com or their app, then this is what the scene commonly looks like:

As you can see, the South-Central China area is strangely empty and the aircraft look to take a circular route around it instead (like this Emirates A380 to Incheon):

So, my question is why don't aircraft fly over that area? Also, I occasionally see some China Air Force aircraft going to that area..

@gochobot my bet is on weather/mountains (they're flying around the Himalayas, after all)

Why are they flying where there are more emergency airports and less inhospitable mountains?

Related: Flexible Use of Airspace in China - ICAO // and // Air force can help combat crowded skies

Also related: China Air Traffic Congestion Worsened by Military Control. China has large amounts of restricted airspace and many routes aren't available for civilian use, especially by foreign carriers. They're making some efforts to improve the situation, but in short: you fly where the government says you can fly.

That said, Flightradar24 may be distorting the situation somewhat. They may have pretty limited coverage over, say, the Tibet region. Flightradar24 says "In areas where Flightradar24 normally have coverage, all major airports are marked with blue airport markers." Note the lack of any blue markers anywhere in this region. There are flights in the area that you just aren't seeing.

@ZachLipton: Very relevant comment, also 8 km mountains create more shadow than usual on existing stations.

Note that the Emirates flight path shown is dodging parts of Afghanistan, not China. The arc you see across China is just the great arc, which is the shortest distance between two points on the surface of a sphere. If you take a look at gcmap.com, you can see what this path looks like for DXB-ICN. The arc shown across China here is almost exactly the great arc path.

@ZachLipton If you look at Google maps, the major population centers and airports in that area are also missing. This is because there aren't any.

@reirab True. I'm not sure what criteria Flightradar24 has for "major airports," but it's got to be more difficult to find volunteers to run their tracking hardware (who have good internet connections and speak English to understand the site) in remote areas like that.

Also I would assume the appearance of an arc has something to do with the map projection used (depicting a 3D sphere on a 2D screen).

While Him's answer is correct, part of the reason that there aren't many airways over central China is just that there's rarely a reason to fly there. Where possible, aircraft prefer to take paths along great arcs, which are the shortest distance between two points on the surface of a sphere (such as Earth.)
In short, there simply aren't many common air routes between city pairs where the shortest path passes over central China. If you look at the first image posted in the question, you will see that the flights into China are primarily flying either to or from Europe or Eastern North America (the ones crossing over Mongolia,) Japan or Western North America (the ones crossing over the Sea of Japan and East China Sea,) India (the ones flying over South China,) the Middle East (the ones flying over North China,) or Australia/Philippines/Thailand/Indonesia/Oceania/etc. (the ones coming in from the South.)
For your great arc path to pass over Central China, you'd need to be going to or from central China itself (which isn't terribly populated,) Siberia (which is even less populated,) the Central Indian Ocean (which is open ocean with Antarctica on the other side,) or the mountainous region between China and India (which also doesn't have a lot of air traffic.) So, there's normally just not much reason to fly there and, thus, not much reason for China to have airways there.
For the specific example that was shown in the question of the Emirates flight, the arc on which its flight path is shown across Northern China is, in fact, very close to the great arc between Dubai and Incheon, which looks like this:

Great Circle Path from DXB-ICN Source: gcmap.com
This map should give you something of an idea for how unpopulated Western China is:

China, as seen on Google Maps Source: Google Maps

This population density map is telling too.

A very good answer. I‘d suggest to add the point that it’s rather difficult for many commercial aircraft, especially twins, to comply with regulatory requirements regarding terrain clearance following engine failure or oxygen supply for the minimum altitudes and diversion distances/times at altitudes dictated by the Himalayas.

This answer, like the others, seems question-begging: "Why don't aircraft fly over Tibet? Because there isn't much air traffic." I think a good answer should explain why the two most populous countries in the world have so little air traffic over their border.

@Hugh This answer does explain exactly that. Nearly all of the population of China lives in the Eastern part of it. Thus, routes between populous Chinese cities and populous Indian cities fly well to the South of Tibet (because the shortest path between those cities is South of Tibet.) Tibet itself is very sparsely populated.

Where does the great circle between Delhi and Beijing lie?

@Hugh That does cross Tibet (since those cities are both relatively far North.) However, according to FlightAware, there is exactly one non-stop flight between those cities (Air China 947/948) and it's only 3x weekly.

Because there is only 1 airway (B345) in Tibet.

Source: Chinese AIP - 15 Jan 2019
China (PRC) creates 2 sets of Aeronautical Charts, AIP and NAIP. AIP is aeronautical charts only listing airways for International flight. It is open for public and foreign organisations. NAIP is a confidential and more accurate aeronautical charts listing airways for both International and Domestic flight. Its standard is different from AIP.

NAIP is [...] confidential -- honest question, why would it be confidential if it's distributed domestically and to international (and presumably commercial) flights anyway? (unless I'm misunderstanding your wording)

@Jules My understanding of what he said was that NAIP lists both domestic and international use airways (i.e. all of the airways,) not that its distribution is both domestic and international. The AIP, which is distributed to international organizations, lists only the international airways.

Sadly, the server on which that image resided appears to have gone offline. :( Any chance you can find another version of it somewhere (and perhaps let SE upload it to its imgur so it stays around?)

According to FlightRadar24, I see Flight TV9886 of Tibet Airlines flying into Lhasa right now.

So, the answer seems to be that they do when they need to.


text:
How do pilots fight jet lag?

Jet lag, medically referred to as desynchronosis and rarely as
  circadian dysrhythmia, is a physiological condition which results from
  alterations to the body's circadian rhythms resulting from rapid
  long-distance trans-meridian (east–west or west–east) travel on
  high-speed aircraft. For example, someone travelling from New York to
  California feels as if the time were three hours later than local
  time. (Source)

As pilots often have to travel between multiple time-zones, especially during long haul flights, with as much as 12 hours of difference between them, how do they fight jet lag?

Pilots have duty schedules, and especially when travelling commercially they must take mandatory rest periods. Its highly unlikely that in the case you presented above, that the same pilots would be flying all the legs.

Crew members each have their own approach to this but in general on the long haul routes, as a pilot you have at least 24h layover, so you can catchup on some sleep, walk outside for a bit (depending on the local time) and then sleep some more so you're fit for the next flight back home. At home you have a couple of days off to recover from the trip.
On the very long flights 13h+ the pilots are with at least 4 so you can do a quick nap on board as well.
As a passenger I cope with the jetlag by looking at the arrival time, do I arrive in the morning I will try to sleep on the plane, will I arrive in the afternoon the I will try to stay awake and go to bed early. By doing so I wake up easily next morning and do not feel jetlagged.

As you say before, #Crew members each have their own approach" about it. I think the key for facing this is try to sleep as much as you can and if is possible, in the local time where you arrive to get avoid quickly the bad consequences of the jetlag. Is very important that you stay hydrate at all times.

Usually, crew member should follow the local time (base/hub time) for their routines on ground, and if necessary, some of the take melatonin to synchronize the circadian rhythms.

The FAA does not recommend the use of melatonin within 24 hours of flight due to its effects. See this FAA document

@RonBeyer "How do pilots fight jet lag?" is not limited to the US... Does this apply worldwide?

@Déjàvu EASA has similar advice, although they just defer to an aeromedical professional

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text:
How is a 436 seater A330 fuel efficient?
Cebu Pacific is a Philippine low-cost airline , which has 6 A330 in its fleet. The capacity of each of them is 436 . As far as I know, one of the reasons why airlines introduce First Class cabins is because its impossible for them to fly with a huge number of passengers and their luggage. It makes the plane very heavy and less fuel efficient. That's why, we don't have any A380 with more than a capacity of 550 , against its maximum of 853. But, how does Cebu Pacific makes profits from operating a 436 seater A330( which commonly has a capacity of 300 people)?

My guess: the vast majority of flights are (relatively) short-range, short-duration, where the expense of the flight isn't offset by a long cruise.

a 4300 mile flight isn't short-range!

Please re-read my entire comment. (i.e. the vast majority...). Cebu cannot afford to purchase some planes for their few long range flights. They set up their fleet to fit their primary flights. Their few long range flights won't be efficient at all, and they'll have to eat the cost or pass it on ... being a low-cost airline, they probably mostly eat it. If they base their fleet on the minority long flights, then they lose overall for the majority short ones.

Emirates introduce 2class a380 with 653 seats soon......

max seating isn't a fuel economy issue, it is a max gross weight issue.

@casey True. I've updated my answer with some calculations to that end. Feel free to comment on it if there's anything I've missed.

First of all, keep in mind that the Philippines has one of the shortest average populations on Earth. Their average passenger weighs a lot less than an average American or European, since weight scales roughly with the cube of height. So, 436 Filipinos don't weigh nearly as much as 436, say, Americans or Europeans, assuming average populations from each group. According to Wikipedia, the average Filipino male of age >= 20 is only 5' 3.5" (162cm) and the average female age >= 20 is 4' 11" (150 cm.) Compare those numbers to 5' 9.5" (176 cm) for males and 5' 4" (162 cm) for females for Americans age >= 20. Considering the roughly cubic scale, that's a pretty significant mass difference.
Second, why would putting more passengers on board not be fuel efficient? It will make the aircraft heavier, but it also means that you're carrying that many more people in one trip. My guess would be that you'll burn less fuel per passenger-mile, rather than more. To get a rough estimate, an A330-300 has an operating empty weight of about 274,500 lb. and it can carry about 175,170 lb. of Jet-A. If we assume the average Filipino weighs about 120 lb. (this seems like a reasonable guess based on my experiences in the Philippines,) 436 passengers would come out to 52,320 lb. while the 293 passengers on Delta's A330-300 seat configuration would be 35,160 lb. So, you're increasing mass before fuel by only around 5.5% while increasing passenger count by a whooping 49%. It would be hard to find a scenario in which that does not use less fuel per passenger-mile (unless, of course, you're overweight and can't take off at all.)

Regarding the issue of avoiding being overweight (and, thus, being able to take off,) Cebu Pacific normally doesn't run routes anywhere near the 6,100 nmi range of a fully-loaded A330-300. This means that they won't need to carry a full fuel load. Even a 10% reduction in fuel load from the maximum capacity of an A330-300 would equal the entire added weight of going from 293 passengers to 436. Even at full fuel load, though, judging from the previously-referenced numbers on Wikipedia, we get:
Operating Empty Weight (OEW): 274,500 lb.
Full Fuel Load: 175,170 lb.
436 120 lb. passengers: 52,320 lb.
14 flight + cabin crew x 120 lb. = 1,680 lb.
Total before cargo: 503,670 lb.
Maximum Takeoff Weight (MTOW): 534,000 lb.
So, that still leaves 30,000 lb. for cargo and anything else that's needed, even if they did need to carry a full fuel load for some reason.

The issue of why Cebu Pacific doesn't offer Business/First class cabins was also mentioned. The reasons for this are mostly their target demographic and their route network (combined with the already-explained lack of weight limit.) While there are many business travelers going to and from Cebu City, the routes on which these travelers are typically traveling are already well-served by several high-end airlines that also offer onward connections to Europe and the Americas (e.g. Cathay Pacific to Hong Kong, Korean Air and Asiana to Seoul, Japan Airlines to Tokyo, Emirates to Dubai, EVA to Taipei.) Additionally, Philippine Airlines also already competes in that space (in addition to apparently offering direct flights from Cebu to LAX now, which I think is a rather recent development.)
With their low-cost model and lack of alliance partners for onward connections, it would be difficult for Cebu Pacific to compete for the already well-served premium-cabin demand in Cebu. Instead, their business model is catered to serving Filipinos traveling between islands and to regional destinations where lots of Filipinos work out-of-country. Last I heard, approximately 10,000,000 Filipinos worked outside the Philippines (around 10% of their total population,) so serving that demographic is not a small market. In case it's not obvious, this is an extremely price-sensitive demographic which is well-served by Cebu Pacific's low-cost model.
It should probably also be noted that, while 436 passengers on an A330 is unique to Cebu Pacific, high-density economy-only configurations in general aren't. Lots of regional-service low-cost carriers offer high-density economy-only fleets, even in less cost-sensitive areas like Europe, Canada, and the U.S. In Cebu Pacific's own region, AirAsia and Tigerair also operate similar high-density, economy-only fleets targeting the same demographic (though, admittedly, AirAsia X does have 2 rows of business-class seats in their A330s, but these are on longer routes than Cebu Pacific normally serves, e.g. Singapore-Australia.)

I don't know if the A330 runs into weight and balance problems with 436 passengers AND full fuel.  It is very common, however, in small planes for the plane to be over max gross weight with all the seats full and also with tanks full.  You have to restrict how many passengers you carry, or make intermediate stops for more fuel.
Since Cebu Pacific has many shorter leg lengths perhaps they can fill all the seats and still take on board needed fuel plus reserves and be below gross weight restrictions.
As you point out, adding business and first class seating reduces the overall weight of the passenger load.  On a weight restricted flight, that alone will increase overall revenue.

The other constraint is that you can fill those business class seats. No point adding first class seats if you cannot fill them. On a majority short haul operation in a cost sensitive demographic it is not clear if you could sell overpriced seats very effectively. You might hardly get the time to even do a price differentiating meal service.

@curious_cat I think Cebu Pacific uses their A330s for more moderate to long-haul flights, rather than short-haul. They use their A320s for short-haul stuff (which is the majority of their business.) You're right, though, that it would likely be hard for them to sell the business or first-class seats. Cebu Pacific is a low-cost carrier that mostly serves the domestic population of the Philippines. I'm guessing the majority of their passengers on these new long-haul flights are Filipinos who work overseas. A full 10% of the Philippine population works outside the Philippines (over 10M people.)

While adding weight to an aeroplane increases fuel consumption because the wings have to work slightly harder and the nose has to be slightly higher which increases drag, and thus an higher power setting is required. So adding even one person is not fuel efficient compared to one less person. But the money received from that extra person will outweigh the additional fuel required.

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text:
Why is braking action (with Anti-Skid) best when the wheel rotates at ~85% of the actual speed?
During my ATPL training the subject of tires and braking was discussed.

I understand the principle of the anti-skid and also the differences between aircraft and similar systems in cars.
Physics also thought me that static friction is greater dynamic friction.

The script mentions that it has been shown that the maximum braking efficiency is obtained when the wheel rotates at a speed of 85% of the ground speed.
[Clarification: imagine a identical tire wich rolls on the surface without any resistance/braking, this would be 100%. Every bit of slip therefore reduces the rpm. ]
Why would this be beneficial?
My ideas so far are:

that if some slip occurs braking is mostly in the static friction range but some energy during braking is also put into deforming the tire (and thereby heating it) and possibly ripping small pieces of rubber (on a really small scale) off the tire.
In order to find out where the tire begins to slip it actually has to slip, so in this process of: raising the pressure on the brake and if slip occurs, reducing the pressure, on average a slip of 15% occurs- whixh means a tire speed of 85%.

Is one of these correct?
Are there any other factors and processes?

this is unclear " the wheel rotates at a speed of 85% of the ground speed." one is a rotational speed (deg/s or rad/s) and the other is a linear speed (m/s). Did you mean " the wheel rotates at a speed such that the outer rim has  a speed equal to 85% of the ground speed." ?

Tire-road dynamics at speed are described by the Pacejka's "Magic Formula", so called because

there is no particular physical basis for the structure of the equations chosen, but they fit a wide variety of tire constructions and operating conditions.

This empirical description was developed using regression analysis and consequently has no theoretical basis as to why it works, but it does work and is widely used. You may not like the answer that 85% is best because that is what the formula says.
The reference gives the parameters necessary for calculating the peak longitudinal force and corresponding slip. ABS systems attempt to balance a peak slip ratio with vehicle directional control, resulting in an ideal ratio between 0.1 to 0.3. (which is 70-90% of ground speed using your terminology)

source
I would modify your statement #2 to say that in order for the ABS to know when the tire begins to slip it has to know when the tire does not slip, which allows the determination of unbraked tire speed from which the desired slip can be calculated. I think this is one reason for pulsating brakes when ABS is active; the ongoing determination of zero slip speed as the vehicle decelerates.

Great find on that graph.

In the case of Maxaret, the pulsing was purely a mechanical side-effect. It turned off the brake every time the wheel slipped 60 degrees, so it pulsed at 6 times the current RPM.

@MauryMarkowitz What does 'slipped 60 degrees' mean?

Too long to explain here, see: https://en.wikipedia.org/wiki/Maxaret

Maxaret is a now obsolete purely mechanical ABS designed in the 50's that used a control disc with a one way clutch that would spin up with wheel on landing. When brakes were applied and the tire began to skid (the wheel began to lock) the disc would advance relative to the wheel. At 60 degrees of advance the disc activated a hydraulic valve dumping pressure from the brake circuit stopping tire slip and the cycle repeated.

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text:
Will Lockheed Martin Flight Services send me ACAS, EasyActivate™, and other text messages if I file my flight plan through ForeFlight Mobile?
ForeFlight Mobile users who file flight plans without being authenticated to CSC DUATS will effectively file through Lockheed Martin Flight Services (LMFS).
Considering that the LMFS route does not require my personal  1800wxbrief.com credentials (unlike filing through CSC DUATS), will additional services connected to my LMFS profile such as Adverse Condition Alerting Service (ACAS), EasyActivate™/EasyClose™, Close Reminders, ATC Notices, and Surveillance Enhanced Search and Rescue (SE-SAR) be accessible through my mobile phone?
In other words, will Lockheed associate my ForeFlight flight plan with my LMFS profile in order to send me text messages with information about TFRs, links to open and close flight plans, and so on?

Is it still about aviation... with trademarks everywhere?

@mins  Certainly looks like it to me, yes.  Part of being a good pilot is knowing how to use the tools you have available and understanding their limitations, and things like DUATS are ForeFlight are tools that lots of pilots use.  This isn't exactly promoting Joe's Little Flying App; I doubt Lockheed Martin needs to come here for "free advertising" of their services.  Looks like a valid question to me.

I can't answer your question, but the simplest thing may be to try it if you're already an FF user, or ask them if you're not. I didn't see anything relevant in their FAQ.

PIREP: I filed through FF today on a quick out-and-back XC. The plan didn’t show up in my plans on 1800wxbrief.com, and I did not receive the text messages as when I file through Lockheed.

Based on my personal experience, the answer is NO (as of the time of writing). I use both systems regularly, and have discovered the two do not share flight plans at the user account level. ForeFlight uses its own account (and not individual user accounts) to interact with Lockheed Martin Flight Services. Because of this, it appears that LMFS has no way of knowing which user account is associated with a flight plan filed through ForeFlight.
Identifying data within the flight plan itself (i.e., name and phone) are not processed by the filing system, merely stored for later retrieval if needed. I mention this because LMFS can (upon request) associate tail numbers with a phone number, so that when you call them on 800-WX-BRIEF your profile comes up on their screen automatically (though I have found this to be less useful than one might think).
In order to use the services you have identified, you will need to file your flight plan directly on the LMFS web site (and have your notification settings configured properly).
With that said, all of these functions (with the exception SE-SAR), have been available directly within ForeFlight for some time:
ACAS/ATC notices - if configured by the user, sent via push notification (http://blog.foreflight.com/2014/11/24/6-5-brings-flight-notifications-and-notam-advisor/)
EasyActivate/EasyClose - flight plans can be amended/canceled/activated/closed within the File & Brief window (http://blog.foreflight.com/tag/flight-plan-filing/#attachment_4045)
Close reminder - sent via push notification (https://support.foreflight.com/hc/en-us/articles/205052928-What-are-push-notifications-)
Over the past couple of years, ForeFlight has been aggressively working towards tighter integration with LMFS, so I would expect additional functionality to be forthcoming (purely speculative, since they are very tight-lipped about upcoming enhancements).
UPDATE:
It looks like LMFS now offers integrated services with a number of providers (but not ForeFlight). My guess is ForeFlight doesn't allow it because it was already offering the same services and now needs to figure out a way to ensure users don't get duplicate messages:

Hello, my name is Daniel and I work for ForeFlight, your comment is accurate as of the time of this comment. Right now we do not integrate with Lockheed's "user account mechanism", for lack of a better phrase. Stay tuned!


text:
How are the costs managed in a codeshare?
How do the airlines manage the costs invovled in a codeshare?
As all airlines are selling tickets, (might be at different prices) but only one of them is operating the flight.  So, how do the airlines decide who will pay how much for the crew, fuel and catering and who will earn what?
And how do you justify:

When an airline sacrifices its capacity to other airlines as a code share partner, its operational cost will generally be reduced to nil. (Source:Wikipedia)

Possible Duplicate: Why do multiple planes arrive from the same airport at the same time?

Short answer: multiple airlines don't operate the flight. One airline operates the flights and the others just have an agreement to market tickets for it. Operationally (callsigns and crew included,) it will be no different from any other flight on the operating carrier. How the revenue is shared probably isn't on topic here and usually isn't made public anyway. For more info, see the question in Farhan's link.

The good question is how they work out the costs from shared routes. If you were to book the flights separately they would almost certainly be more expensive when you add them up. Do airlines agree a lower cost to complete their leg of the journey? How do they work it out I wonder.

@PaulRedmond That's certainly not always the case. Sometimes it's actually cheaper to book the flights separately. At any rate, airline pricing schemes are complicated, somewhat secretive, and probably not really on-topic here. For whatever it's worth, though, ticket prices usually are based on origin and destination, often completely ignoring what route is used to get there.

@reirab Fair enough, thanks for the input.

Do you mean codeshare? (https://en.wikipedia.org/wiki/Codeshare_agreement)

I wouldn't necessary believe a quote from wikipedia.

hope this is not marked as off-topic now...

As the wikipedia article clearly states, there are several types of Codeshare Agreements :

Block space codeshare: A commercial (marketing) airline purchases a
  fixed number of seats from the administrating (operating/prime)
  carrier. A fixed price is typically paid, and the seats are kept away
  from the Administrating carrier's own inventory. The marketing airline
  decides on their own which booking classes the seats are sold in (the
  block of seats are optimised just like another aircraft cabin).
Free flow codeshare: The airlines' inventory and reservation systems
  communicate in real-time by messaging, commonly IATA AIRIMP/PADIS
  messaging (TTY and EDIFACT). A booking class mapping is defined
  between the airlines. No seats are locked to any of the airlines, and
  any airline can sell any number of seats.
Capped free flow: Basically the same as above, but a capping (max
  number of seats) are defined for each of the marketing airlines
  participating in the codeshare with the Administrating
  (operating/prime) carrier.

In these cases, profitability of the Airline Marketing the other airline's tickets is possible in any of the following ways:

There might be an agreement with the Carrier Airlines where the Marketing Airline gets to sell the tickets at the same rate as being sold by the Carrier Airline,but the Carrier Airline sells the tickets to the Marketing Airline at lower prices. This helps the Marketing Airline to generate revenue and improve its indicated (apparent) frequency on the given route. The Carrier Airline is benefited in a way where its tickets are sold on more than one portals, so better visibility (Marketing) and hence the name.
Now a days alliances like OneWorld are being formed, where multiple carriers come together and form codeshare bases to mutually benefit each other.
The Marketing Airline might even sell the tickets at a cheaper price than the original Carrier Airline, just to establish its base in the route before starting its operations, so that when it starts its operations, people already know about it. hence, without deploying planes for the route, it can already have an established consumer base.


text:
How can I find the communication with ATC following an aborted landing?
On February 7th, I was on a UA 4694 from DEN to SAF, upon approach the landing was aborted; upon second approach, we heard the landing gear come down, which we did not hear on the first approach; the rest was uneventful.
I just reviewed the "Live ATC" recording for that period, and there is 90 sec. period of complete silence on the ATC recording, between the Tower giving permission at 16:05:02 to land and at 16:07:07 instructing UA3649 to 'turn left at Delta 1, and contact ground". It appears that there is no recording of the aborted landing, second approach, nor any other communications from the tower during this approximately 90 second period.
Would the ATC recording include communication related to an aborted landing? If yes, how can I find it?

Reportable to whom? If in fact the landing gear had not been lowered, then everybody who needs to know about that incident is already well aware of the situation.

What makes you think there was a mistake made here? Passenger estimates of speed and distance are notoriously unreliable, but if you were actually at 250ft above the runway the aircraft wasn't going to land anyway. More likely, the crew were asked to go around by ATC long before and elected to fly a missed approach as the easiest way to remain in the traffic pattern.

Your edits to your question add very little.  No airliner could fly a missed approach, reposition, fly a second approach and land in the space of 90 seconds. Something here doesn't add up, and I fear it's your understanding.

To add on what @ReddHerring says. Flightaware shows part of the goaround ( https://flightaware.com/live/flight/UAL4694/history/20190207/1835Z/KDEN/KSAF ) and it lasts the full final 6 minutes of the available recording, from 16:07 to 16:13, and it shows that the plane landed even later. Moreover, UA3649 does not land in SAF, being a RDU-ORD-LAN flight

This question is being discussed on meta: https://aviation.meta.stackexchange.com/q/3756/1467

It takes a lot to forget to lower the gear.

Both crew forget to do the pre-landing checklist.
Both crew ignore the gear warning horn that goes off when thrust is reduced with gear up when configured for approach.
Both crew ignore the Ground Proximity Warning System audio callout "Too Low, Gear", which goes off at about 400 ft when descending with gear up.

Not to say it doesn't happen and it's possible the crew was so preoccupied with something they missed all of that (it happened to a Brit Air crew landing a CRJ200 with flaps stuck at zero, who managed to actually land wheels up), or maybe only reacted when the GPWS went off.  It's also possible you misinterpreted something or didn't notice the gear going down the first time assuming it did.
In any case, I don't believe there is any kind of formal reporting process for passengers for that kind of event where passengers report on crew performance issues.  Write to the airline and quote the flight number, time and place and ask for an explanation.   You'll probably get a lawyerly answer that is vague, but reading between the lines will hint at what happened. No harm in asking.

Thanks! will do!

You could also find the LiveATC recording of the tower frequency at the time. Typically the controller would ask the pilots for the reason of the go-around.

It takes a lot to forget, but circumstances, stress and haste can help a lot too: Malév 262 at  Thessaloniki in 2000. It came unnoticed by Greek ATC and lives were likely saved thanks to the prompt reaction of another aircraft pilot.


text:
Can a glider make a go-around?
Since gliders don't have engines, is it possible for them to go around? Are there any extra features on a glider to try to prevent that situation from happening?

I'm not a glider pilot, but I've seen them fly the entire length of a runway at around 10 feet up, then pull up, do a 180 and land. It was always a planned maneuver as I understand it. It's a matter of energy management, obviously.

Some gliders do have engines.

@DJClayworth: you learn something every day! didn't know that, thanks :)

@DJClayworth Well, that would be a motorglider!

@Terry I think of those as a glider military break. They can be done at 1000agl as well.

Yes, but it will not be landing at the place desired.

No. A (pure) glider cannot make a go-around in the way a powered machine can. The glide path can be influenced by airbrakes, flaps,  chutes or slipping, but mostly those are for reducing your L/D, i.e., steepening the approach (you win again, gravity!).
Gaining height without updraft is only possible by converting kinetic energy (speed), and that gain is limited by the stall speed. So while you can rise a few meters when you pull up from landing airspeed, you will find yourself way too high above the runway at minimum speed and hoping for the best.
The highly enjoyable* spectacle of a low fly-by of a glider is achieved by starting with really high (unlandable) speed which is then converted into height and shortly followed by the inevitable landing**. For some older (mostly wooden) gliders, even this is not a very good idea because they combine a lower VNE with lower L/D ratios,  leaving you low and slow after pulling up from redline speeds.
In a glider, you get one chance for a smooth landing (freak thermals excluding). But a properly trained pilot gets used to this very quickly. A proper landing procedure together with brakes, flaps, etc. will bring you down safely.
*but not necessarily safe or recommended
** unless you catch a proper thermal or dynamic updraft.

video link broken; can you help?

@Alexandria pity the original video got removed. Updated with a fly-by compilation.

The gees must be super awesome!

No, a glider can't make a go around, but if they are going fast enough they can make a low pass (which looks like a go around), but that generally means that they won't be in a position to actually land even if they wanted to.  The key to safely managing and landing a glider is energy management.  When coming in to land it can't be too slow and low OR too high and fast (only one factor can be adjusted by trading altitude for airspeed or vice-versa).
Most gliders have airbrakes or spoilers which are used to bleed off excess energy.  A typical approach will have them deployed about half way when on final to land so that they can be used like a throttle in an airplane.  If they get low or slow, the airbrakes can be stowed in order to increase the glide ratio (just like adding power in an airplane).  If they get high or fast the airbrakes can be extended further and/or the glider can be slipped in order to decrease the glide ratio (just like reducing power in an airplane).
Other than the very high glide ratio and no engine to go around with, they land very similar too an airplane. If you've never flown one, I would highly recommend it.  Not only is it fun, it will make you a better overall pilot!

My answer is mostly redundant, but more answer are good for the beta in any case. Uh, and +1 for recommending soaring for becoming a better pilot :D

It's worded a little differently and I think that it adds to the question!   :)  The funny thing is that I was coming to the site to add a link to a video of a glider fly-by this morning, but you already provided one so I don't have to look one up!

One cannot have enough Überflüge - add away!

Yes,there is one scenario when they can. At our club we are on the top of a hill and if the ridge is working you can abort the approach close the airbrakes and run over the threshold onto the ridge. In fact our low cable break briefing is land straight ahead or takeoff.

Nice (esp.  the last sentence) ! Care to add some photos or video?

Yes, please add a video or pic ;)

I have also heard of glider ports at the top of hills and one can go around by landing at a different runway at the base of the hill.

I have heard of someone doing this at The Mynd :)

Here's a forced example:
In 2006, I asked a CFIG what he would do if the rope release failed for both the glider and the emergency release on the tow plane.
He suggested we try the exercise of seeing what it would take to land on tow. (It turns out, it is REALLY easy to overrun the tow plane when on descent).
So, technically, I have 3 glider touch-and-goes logged in my logbook.

In Germany in the 90s, such a “Schlepplandung“ used to be a regular part of the tow training, not sure if this is still the case.

Very cool. In actuality, I would break he rope rather than land behind the tow plane.

Having done it, I think I'd rather just land. But if I hadn't had the practice, then I'd rather break the rope too.


text:
The root cause for Boeing 787 Dreamliner battery problems
Wikipedia's B787 article states that:

The causes of the battery failures are still unknown. There is still concern that because the root cause of the fires were not identified, the solutions put in place by Boeing will not be able to cover the full range of possible failure modes.

But 787 was still cleared for flight after it fixed the "Fire Propagation" problem by correctly packaging its batteries in a fire resistant material.
My question is :

What is the actual cause of such Battery problems? (If it's known?)
If Boeing is not able to resolve the root cause of the fires (according to Wikipedia), then is it safe for the Dreamliner to be allowed to fly?
Because what they have done to resolve the problem does not appear to be a permanent solution, but more of a temporary fix.

The cause is not confirmed, but the containment measures taken are satisfactory and ensure safety in case of battery fire.

I don't see what the question is. We know that the cause is unknown; the regulatory authorities feel that the containment measures make hte plane safe enough. What is left?

I firmly believe that this is an answerable question, and we do know what caused fires in batteries. See this question, and then this link

@anshabi Neither the question or the article you point to states conclusive proof of cause of the battery failures. This is an unanswerable question, for now.


text:
What would happen if a Russian TU-95 had an engine failure or other emergency close to the United States?
Russians often fly the Tu-95 for long distances, in some cases reaching the California coast.
What would happen if they had an engine failure or another emergency Considering the aircraft's age, an emergency is not a very remote possibility.

Would the Tu-95 land in California?
Would it rather try to come back home on 3 engines?

I don't get the question: are you asking what happen if you have an emergency? Why would it be different than with any other aircraft?

@GianniAlessandro: It would be different for political reasons. And because the reasons are political, it does not belong here.

See this question: replace "North Korea" with "California" and "airliner" with "Tu-95" and the basic points will be the same. Although as others have posted, if one engine fails in a four-engine aircraft, that isn't necessarily a full-on emergency requiring an immediate landing.

I changed the question back to what I believe the OP was thinking about according to the early revisions...

The answers to this question would be similar to the one about an emergency landing in North Korea. The big difference would be that the plane is Russian military property instead of a corporate-owned passenger jet, and you're dealing with the American government instead of the North Koreans, so the crew of the aircraft are much more likely to make it back home (whether or not the U.S. keeps the plane depends on U.S.-Russian relations at the time).

Losing an engine on a 4-engined aircraft is not overly dramatic. In fact the P3 Orion actually intentionally shuts off one engine in flight to conserve fuel- it's more efficient to run three of them at higher power setting.
I doubt that they would put their aircraft in a position that they could not withstand an engine failure. From Kamchatka to California is it around 6000km max one-way; The TU-95 has a range of 15,000km.
As for potential political mess, you can see what happened when a Chinese J-11 Fighter collided mid-air with a US Navy P3 Orion back in 2001 in what is known as the Hainan Island Incident.
A British Airways 747 lost one engine out of Los Angeles a few years ago, and almost made it all the way to London, but diverted to Manchester (although that event did cause a lot of controversy).

I'm not sure the 747 is as relevant, though - I think the point of the question is "The Tu-95 doesn't have a flight plan to fly to the US, would it be allowed to enter". You answer regarding an engine failure and (likely correctly) point out that it could just turn round and return to base: but not what would happen in another emergency where it couldn't easily return (ie a return would be risky)

@JonStory Perhaps the crew would prefer to try for Canada if at all possible - but yes, an engine failure would probably not be enough to force an emergency landing. An engine on fire, perhaps?

I imagine that would be a cause for concern. I think the point is that in an emergency America would probably, in theory, allow the Tu-95 to land (escorted) at a USAF base... I assume, anyway. That's the question, IMO

Two parts here: what would the CREW want to do (land in US, Canada, go back to Russia, etc), and what would the US let them do. The Russians probably have guidance on how bad an emergency has to be before you do something drastic like landing in the US; it'd be speculation to fill in those blanks. For the US, if the aircraft is in distress, yes they'd let them land rather than force them to ditch. As mentioned, what happens to the aircraft depends on lots of political factors. But, SALIENT POINT FOR AVIATION.SE: yes, they'd be allowed to land.  NOT an "off-topic" question at all!

This link discusses an ICAO member state's obligation to provide "practicable" assistance to aircraft in distress.

The US would love to have the Tu-95 land here. It's basically a free copy of the plane for US intelligence to examine.

To answer the more general case of what happens if a military plane has an unrecoverable emergency near the airspace of an unfriendly nation. The crews has a number of choices:

Declare an emergency and land in the unfriendly nation. The unfriendly nation is obliged (morally and under international law) to allow them to land. However the plane and its crew then become interned, which is a bit like being a prisoner of war, without the war. What happens then is up to the interning nation, and depends on the state of relations with the aircraft owner. The plane may be returned after some diplomatic maneuvering, possibly following a detailed technical examination. Or it may not. The crew may be returned, again possibly after some sort of questioning. Or they may not. During the Cold War, US pilots downed in Russia were sometimes held prisoner for years, and interrogated extensively (to put it mildly).
Do their best to make it home or to a friendly base, even if such a hope seems doomed. This is likely the orders of a plane with highly sensitive technology, or anything else the nation really doesn't want other nations to get their hands on.
Abandon the plane in such a way as to give the crew a reasonable chance of survival, but assuring the destruction of the plane, such as pointing it out to sea and ejecting.

Being shot down after flying over a foreign country without permission is a wholely different situation than having an emergency near a foreign country and landing there with permission. Or are you saying that American pilots during the Cold War had emergencies near the USSR, landed there with permission and were held prisoner for a long time?

@DavidRicherby I cite those as examples at the extreme end of what might happen.


text:
Does official source of data about air routes exists?
I'm interested in the information about air routes of all the world. I need information with following features:

it must be official (not stolen, without violating any license);
it should be in digital form;
it should be in WGS84;
it should cover all of the world;
it should be free (no payment);
it shouldn't be detailed (just main routes);
it shouldn't be actual (current), one or two years outdated is appropriate.

I've realised that some kind of this information is published by ICAO at the AIP, but I can't find it.
So my question is: whether such information is available and where I can find it?

As you probably know, companies like Jeppesen charge a fortune for current information of the above sort. Your only hope of finding it for free is the fact that you're willing to accept outdated information. Having said that though, I'm not sure where one would find outdated, accurate info.

Such information is not available, for free, on a world wide level.
If you are willing to spend some money, you should have a look at Navigraph, which provides such information on a world wide level, for hobby use.
However, most countries now make their AIP publically available on the internet. Simply search for "[country name] AIP" to look up an AIP for a specific country.
In any AIP, you want to look at part 3 of the ENR section. Usually ENR 3.1, ENR 3.2 or ENR 3.3. Here is an example of from AIP Denmark: AIP Denmark ENR 3.3 - RNAV routes
This information is digital, official, up to date, free and in WGS84 format. However, you will have to look it up for every country.
If you are looking for a visual overview of airways and RNAV routes in Europe, a good place to start is the Eurocontrol regional charts.
You should also check out SkyVector

This information is digital, when I say about "digital", I mean format which allow automatic processing of that data (without human), something like XML but not PDF or image. Anyway your answer is very useful!

I'm afraid you won't find anything like that for free, but check out Navigraph as I mentioned in the answer

I'm afraid you won't find anything like that for free, free is wish, but not requirement (I've tried indicate this by using "should" instead of "must").

I a m not sure about the WGS84 convention requirement, but some websites do provide flight data (which might not be up to date), but is fairly new (2012).
Here is a link to one of the websites which provides data about 669 airlines, 3310 air ports covering about 56749 routes. You can also have a look at this and this

Thanks for your answer, but unfortunately information which you refer does not contain full data (all points) about routes, but only about input and output airports.


text:
What are those little rods that stick out of a planes fuselage?
I noticed quite a few of them around the nose and cockpit area of a plane when I was at the airport and wondered what they were for, could someone please help.
THERE'S A PHOTO BELOW.
Thanks

Generally speaking you are most likely looking at the Pitot tubes

Some angle of attack indicators also look quite similar and in the case of some of the A380 the Pitot tubes and angle of attack indicator are combined into one unit.


text:
Building optimal RC flying wing
I have an EMAX motor that operates at maximum efficiency generating 200g of thurst. This is the only fixed parameter I have.
How do I find the most efficient wing design for this flying wing, considering my motor should push 200g in order to operate on its most efficient range.
I know the bigger the aspect ratio, more efficient the wing will be and more flight time.
I would like to use a KFm airfoil (cause of its simplicity on building it).
How an RC hobbyst (I am a mechanical engineer too), with not much knowledge on drag, lift coefficients... can come up with an optimal design?
EDIT:
Sorry for being too broad. Let's specify better:
1) my electronics weight (motor, esc, battery, servos...) will be at 50g;
2) I want to use a foam board, typical on rc plane community which is thin and lightweight
3) I want to optimize for flight time, not flight distance.
I am really lost at this, even after searching a lot. I know the vector diagram of my plane (weight is down, lift is up perpendicular to the wing, drag parallel to the wing and I know there are many types of drag but I would assume only the most relevant drag which is the one generated by air deflection and thrust is also parallel to the wing pointing forward).
The only vector that I know how to quantify is thrust and weight. The other 2 I am very lost!
EDITED so it can received answers.

You are going to need to decide what it is you are optimizing, for a start. As it stands this is way too broad. What is your takeoff weight? Is efficiency the most important factor? What is the mission? In theory, an infinite-span wing would be a very efficient solution (if you manage to stabilize the flying wing without sweep), but I have a feeling you're not after that answer.

You question is really broad. It would be easier to answer specific question about specific part of your design. You may also include your current knowledge so that answer is more adapted to you current understanding.

@AEheresupportsMonica I edited my question, sorry for not being specific!

@ManuH I made the question more specific, hope this clarifies!

Sorry, another nitpick: a Kline-Fogleman airfoil will not lend itself well to a flying wing, I'm afraid. If it has to be a flying wing you will need some combination of a reflex airfoil and wing sweep to achieve longitudinal stability. I will assume you can actually fit your avionics inside a fuselage or pod, otherwise your airfoil will also need sufficient thickness to not only carry the bending loads caused by lift, but to also house the electronics. Otherwise you could drop the flying-wing requirement, they are not as great once you look past the nice aesthetics.

@AEheresupportsMonica yeap! I know flying wings are not great on efficiency mainly because of the reflex. However they are a lot easier to build, lighter and easier to carry arond when compared to normal planes with fuselage/tail. Because I know flying wings are already not optimal, I would like to calculate the best chance I can get with then!

Just buy a Zagi: https://zagi.com/

You don't need an optimal design to have fun.  General guidelines:  Your model should weigh around 500 - 700 grams.  Wing span around 1.5 meters.  Chord around 0.2 meters.  But you really need to nail down your speed envelope.  Too fast will be difficult to control, too slow and it's an indoor delight but an outdoor nightmare (due to wind).
A good place to start would be a chunky reliable design similar to a Piper Cub or Cessna 152.  Shorter more highly loaded wings should help you find the sweet spot of around 7 to 25 mph, which is good for R/C planes.
Build an engine/battery/servo frame that can easily change out wings and empennage as you fine tune your design with gliding and powered flights.
You may wish to start with a slightly cambered KFm 1.  Slower speed and lower wing loading should give more endurance, but will be blown around by the wind and will actually be less efficient distance wise into the wind.  Go conservative on your first build.
Control surface dimensions can be had from foamies at your local hobby shop or R/C club, and more information is available at the RC Groups website.

thank you so much! Very good advices :) But I still would like to get the math working with this new plane I wlil build. I already built hundreds of foam planes and I see that pretty small changes on the design have strong effects on performance (flight time). So this time I would like to stop spending time building planes till find a good performance and start researching/calculating it before building!

@Samul  you may consider moving from foam to balsa, which is more rigid and lighter.  Also, the KF will not be as efficient in slow flight, the one pictured was superseded by thin undercambered wings.  Building from scratch, only the wing ribs take much time, sheet balsa can be easily folded right over them.  The conventional tail is good to have for control at lower speeds, but a design like the E-flite Opterra may interest you.


text:
Are Ground Crew Airline or Airport Personnel?
Are ground crews (baggage, tug operators, fuel, aircraft parking guides, etc.) hired by the airline or by the airport authority? I’ve always been curious.
What are the norms worldwide vs US? Small town Regional vs International Hub?

A useful extension on this question may be to look at world wide norms, and possibly differences in small regional airports vs where a carrier has their hub. [I've seen a mix of jackets at times in various airports across Canada, but can't speak with any authority as to what's normal.]

@TheLuckless I went ahead and edited my question to add that. Thx for the suggestion! :)

I’m sitting here in MCO waiting on my flight and noticed almost all ground crew at the gates have neon vests on with airline logos, but does that necessarily imply they are airline personnel? Or simply airport personnel assigned to service that airline’s gates?

Ground crew are typically employed by a handling agency, which is a company dedicated to performing ground handling of aircraft (exactly the things you describe).
Some airports have several different handling agencies. Have you ever noticed, when waiting for your luggage to arrive at an airport, that there are several different help desks to choose from, depending on your airline? Those are the different handling agencies at that airport.
At a given airport, a certain airline will typically have a contract with just one handling agency. Sometimes, airlines have their own handling agencies. The exact structure can vary.
Smaller airports often do not have third party handling agencies, but instead offer handling services directly to the airlines. In such cases, the ground crew is employed directly by the airport, and could also have other tasks, for example as airport fire fighters.


text:
Is the Batjet Design Physically Feasible?
I realize the plane is fictional. However, in the Batman Animated Series by Warner Bros, we see this Batjet.

So this got me thinking (and I'm not a physicist): is this air frame configuration even possible? Has a "rounded", forward-swept wing design like this been attempted before? Or would a design like this never actually fly?
Any real-world examples that are similar in nature?

@RyanMortensen what?

"handwavium. Noun. (uncountable) (informal, fiction) "Any hypothetical but unobtainable material with desirable engineering properties."

@RyanMortensen ah I see.

With enough power, anything will fly, as a cursory visit to any R/C group will attest. Are you interested in hearing that or is this about whether this design makes sense from some perspective?

@AEheresupportsMonica I was more interested in whether this design makes sense. Basically, is it a horribly inefficient waste of energy just to make it fly, or would it theoretically be amazingly efficient?

Things that work amazingly well tend to get developed.  Those who are working hard to get rich/famous/whatever don't tend to ignore good designs "because it's already been in a comic/movie/etc."

I don't want to bypass the QA of the site by answering in a comment and I don't have time for a proper answer, but long story short, there are good reasons why you haven't seen anything like this IRL.

It's actually not difficult to build a kite like this that would fly pretty well. I believe some good father have built one for his kit over these years, somewhere in the world. Airplanes looks like they do now because others are less efficient, not others won't fly. With enough power, anything flies.

This is actually one of the few good "hypothetical" questions that's been asked.

Yes, rounded wings have been tested in the past. Probably the most famous example is the Vought XF5U "Flying Flapjack". They work perfectly fine. However, the design as pictured does have some flaws.
Efficiency
The lower the aspect ratio (i.e. wider front-to-back in comparison to their length left-to-right), the more inefficient the wing. This is due to there being a lot of area available for the high pressure under the wing to wrap around to the low pressure on top, creating large wingtip vortices. For the Batwing, this would be doubly true, as a large part of the wings have edges on the inside, almost doubling the effect.
Stability
It appears that the engine is either directly behind or directly below the cockpit, putting the center of gravity way too far back compared to the center of lift. This creates an unstable situation, especially at low speed. As the elevator loses effectiveness, the nose of the aircraft will tend to rise, further exacerbating the loss of speed and leading to a stall. Such a stall would be almost guaranteed to be unrecoverable using normal means.
(I say "normal means" because, in the show, the Batwing was shown to have VTOL capability, meaning it has vents in the bottom to redirect thrust down and hover. So, it would be theoretically possible to use engine thrust to rotate the plane nose-down and recover from the stall. If the engine fails, though, this airplane becomes an absolute deathtrap.)
Control Surface Effectiveness
Unfortunately, the animators of the show never animated the control surfaces, so we're left to guess where they are and how big they are. If they're in the standard position in back, that puts them close to the axis of rotation (which goes through the center of gravity, see above), limiting their effectiveness.
The elevators could be moved to the leading edge, but the slipstream on them would cause issues with flutter, and it would take a huge amount of control force to keep them from being pinned at their limits. This also wouldn't help the ailerons (because they'd still be close to their axis of rotation) or the rudder (because there's nowhere to put it other than that big mohawk structure coming off the top of the cockpit).

So, in short, it's possible, but not in any way practical.

The XF-5U never flew. Its equally rounded predecessor was the Vought V-173 prototype, which did fly.

This very good answer could be improved by mentioning directional stability as well.  It might actually have a chance if the cockpit, engine, and vertical fin were reversed.

Rounded, forward-swept and reverse-tapered designs have all been flown, but never put together.
A rounded example has been given, though it was propeller-driven. The jet-powered Avro Canada VZ-9 Avrocar was a slightly weird VTOL concept which failed to fly properly. Another intriguing one, though intended to be rocket powered, was the Pye Wacket hypersonic missile project.
Forward-swept fast jets include the Grumman X-29 and Sukhoi Su-47.
The Republic XF-91 Thunderceptor had reverse taper. It did what it was meant to do, which was to avoid pitch instability near the stall. But, for rather obvious reasons, it was structurally impractical. The Batjet would suffer the same problem.
The other problem with the Batjet design is centre of mass. It needs to vary from around one-third chord at subsonic speeds to one-half chord at supersonic speeds. The cartoon design has it too far back at around the two-thirds chord position, causing a strong nose-up tendency. Jet thrust at the rear would have to be angled sharply downwards to maintain trim, and this would militate against speeds much higher than a helicopter.


text:
Can a civilian purchase a new (Not Retired) fighter jet?
Let's take a jet like the F22 for example. Strip all the classified systems/weaponry out of it (civilian wouldn't need that), and just leave the basic aircraft itself.
Could a civilian technically purchase this aircraft for personal recreational use/travel? Or are these exclusively contracted to the military? How does that work legally/technically? I've always been curious.
There are multiple cases of wealthy civilians purchasing USED fighter jets, sure, but I'm talking about a wealthy civilian who can afford it ordering a shiny new (not retired, there is a difference) personalized, non-armed F22 for personal use. Is that even a legitimate premise?

The F22 cannot fly (or even start the engine) without the classified systems.   The software that runs the FADEC is classified; the control surfaces are governed by classified software.

ok, I see. I didn't know if technically someone (a Tony Stark-like billionare for instance) could just walk into a Lockheed-Martin office and speak to someone about purchasing a specialized F22 because rather than jetting around in a "luxury Cadillac" Gulfstream, they'd rather flamboyantly jet around in a single-seater "Ferrari", or if that's just a crazy premise in the first place.

There are much older jets that can be purchased (https://www.controller.com/listings/aircraft/for-sale/list/category/10072/turbine-military-aircraft)  But not the newest most advanced stuff.

@Pondlife - that question is different from mine. It asks if a civilian can purchase a RETIRED military aircraft. I am asking if a civilian could walk into Lockheed-Martin and purchase a shiny NEW dis-armed, de-classified fighter for personal use.

If you have the money, it would probably be easier to just (start a company to) build your own, e.g. SpaceX, SpaceShip 1 & 2.

@Jon The answers there already cover everything, don't they? Basically, "No, you can't buy anything that's covered by arms control legislation, which modern fighter jets obviously are."

You can buy a Sukhoi Su-27 used, and it may be possible to buy them new that are unarmed and without any weapons systems. At least 2 are registered currently by a private company in the US.

There are several reasons that an individual would not be able to purchase a fighter jet new off the line.
The manufacturer is focusing on meeting requirements for their current production contracts. A private order would basically be a one-off for them, which adds complications to production.
Although it's possible to "de-militarize" a military jet, that doesn't mean any airplane could be delivered to a civilian. There may be basic aircraft systems that have restrictions. The US allows most military aircraft to be exported to certain countries, but the F-22 was never allowed for foreign sale, not even with limitations on what systems are installed. Sales to private individuals would have even more restrictions.
Once the aircraft are available "used," the technology may be less protected. Even then, many challenges remain for operating the aircraft. A pilot would need to get training on the aircraft which would be hard to find outside of the military. It would be very difficult to find a location that is qualified to provide service and repairs on such a private plane. Any service would also be fairly expensive. Military jets require much more maintenance time per flight hour than other aircraft. They are also designed to be operated with the help of a ground crew. Of course there are some military aircraft in private hands and they have dealt with these challenges. But it takes an owner with the dedication (and mostly the money) to make it happen.
For most any purpose, there are much better options. Business jets are much more comfortable, and you can have someone else fly if you want. They'll also be much cheaper to buy and operate. If you want something more maneuverable, you can buy something like the L-39, a jet trainer that can be found used, or possibly new. Especially used, it will still be much cheaper than a new fighter and can do just about anything a modern fighter could. A modern fighter can go faster and turn harder, but that's where the special training and equipment become a challenge.

Certain jets, yes.
But not the F22.
See current listings:
https://www.controller.com/listings/aircraft/for-sale/list/category/10072/turbine-military-aircraft

While great answer beyond doubt, the newest aircraft I see is 1995 CANADAIR CF5D so not fully sure.

A bit of a loaded question, like how are you defining the aircraft; without all the systems and weapons is it still the same aircraft? Do you require the ability to use certain abilities, like supersonic travel or is it more of a collectors item?
Anything can be bought if the stack of cash is tall enough, even permission to own a particular jet. Though this permission may have details like it must stay in the national airspace, file special flight plans so the location is always known, and maintenance can only be performed by certain companies.
You could even get an F22 built with custom non-classified flight systems, of course this custom development would cost a bit extra, really it would essentially be ordering a one-off experimental that looks like an F22, and we are back to how you define the aircraft. Plenty of other types that are less classified are still in production, such as the F18 and F16 would likely be available to a civilian with more reasonable modifications.
Assuming this is for flight over land the speed is limited to less than mach one, and if you don't need the low radar profile, there are better designs for sub-sonic high performance flying. Fighters have many considerations other than pure flight: armor adds weight, aerodynamic effect of externally mounted weapons(and the frame mounting hard-points), weight of the internal weapons, those guns change the balance and useful load, targeting systems, active radar and counter-radar systems, passive radar reflection, heat signature, cameras, flight with damage. All of this detracts from flying performance.

FWIW - If you wanted anything essentially based on a true F22 it would cost you tens of billions to build from new. The cost of reestablishing production is so high that there will never be any more military F22s - unless someone woth far depper pockets that sense stumps up for one privatyely.


text:
What is the reason for KSFO PRM approaches being decommissioned?
In the latest terminal procedures packet dated April 22nd all San Francisco PRM approaches have been deleted.  I haven't seen any notice from the FAA on the decommissioning and am curious what the reason is.  Is there any official documentation on the decommissioning?
Thanks

Not officially, but a friend there said the staggered approaches are good enough and require less staffing.

@StephenS Do you or your friend know how often PRM approaches were used in the past?

Would be nice to mention what "PRM approaches" are. Have no idea (allthough I have good knowledge of general aviation).

@kebs PRM stands for Precision Runway Monitor. It is used for Simultaneous Close Parallel PRM Approaches and Simultaneous Offset Instrument Approaches (SOIA).

Thanks, also found WP link, added in question.

They didn’t use SOIA / PRM everyday pre covid. In fact, even though it was officially decommissioned recently, it’s been several years (2017 maybe EARLY 2018) since NorCal approach has even staffed the PRM scopes or run SOIA Ops. They would only need to staff it when the weather sucks. When a pilots are able to see each other, they are running sideby visual approaches to 28L/R. Some of the foreign heavies will get an ILS with their “pairing” Traffic being on a visual approach. So:

they didn’t need it unless it was IFR.
They need less staffing without it. The controllers have to open up two more scopes when running SOIA operations. The PRM monitor scopes. Without it, they need less bodies. Hence, less money the FAA has to spend.
closely spaced parallel operations or “CSP” replaced SOIA. FAA order 7110.308 allows the controllers to run slightly staggered approaches to parallel runways. It used to require a 1.5 mile stagger. They got a waiver at SFO / NORCAL approach to run a 1.0 mile stagger between airplanes in the same “pair”. Making dual ILS approaches in full IFR conditions practically just as efficient as SOIA / PRM operations. So they don’t need it. Hope this helps!

Welcome to Av.SE!

PRM approaches require recurrent crew training, additional ATC personal (you monitor a PRM controller in addition to the tower controller), and don't increase efficiency into SFO or PHL (which decommissioned their PRM years ago) that much.  Today's airports are being built with runways separated enough to allow simultaneous ILS approaches.
In short - Training cost + Personnel cost > operational savings.


text:
What should I follow, if two altimeters show different altitudes?
My school airplane has a Garmin G5 Electronic Flight Instrument and round gauge altimeter,
but they have almost 50ft differential. The G5 shows 50 feet higher on the same altimeter setting.
So in IFR, when I shoot the approach or cruise flight, my primary altimeter is the G5 so I follow my G5 altimeter.
But my instructor said "you hit the minimum, because standby (round gauge) showing below (-50ft) the minimum..."
In this case should I follow my round gauge altimeter? Even though the G5 is alive?

"my primary altimeter is the G5" Why?

As a non-aviator layperson, I would always chose whichever shows the lowest altitude - I'd much rather find that there's 50ft of unexpected descent left before touchdown, than the opposite!

@Noughtnaut Satellite (GPS) and barometric (normal) altimeters are never used to determine touchdown height, or used at all below the MDA or DH ("decision height"). In that regime only radio (radar) altimeters are useful, and still are not a primary landing aid except for autoland.

The instructor said "you hit the minimum ..." Actually you did, on both altimeters. But, if you use your round gauge as your primary, make sure it is set to the local pressure where you are landing by checking the Kollsman window, and adjusting it as needed.

Take the average between both ;)

The old "man with two watches never knows what time it is" conundrum.

@noughtnaut, as a non-aviator layperson, hopefully you (and 15 others...) learned something from Chris' answer!   I get your point though.  ;)

@RobertDiGiovanni Why such needless nitpicking from everyone? 윤상우 did mention the altimeter setting. In the same way others could be reminding you that one should not just set it to some local pressure but the QNH valid from the locally valid certified official station.

The G5 is not certified as a primary altimeter- its information is advisory only. From a legal standpoint, your primary altimeter is always the certified one- in your case, the steam gauge one.

Garmin itself says:

With the Auto Calibration feature turned on, the altimeter accuracy can range from +/- 50 to 125 feet (same as GPS elevation).

You can draw your own conclusions from this!

authors: Vladimir F Героям слава


text:
What are those devices sitting on top of instrument panel in this Baron?
On this Baron YT video:

what are the two devices sitting on top of the instruments panel, on both sides of the compass?

I though at first it is some kind of HUD (Head-Up Display), but it looks way too small, compared to, for example, this Garmin device.
I tried to zoom in to see the marking on the left one but no success.

It’s a STC head up display angle of attack kit.  In addition to an angle of attack sensor being installed on the exterior of the aircraft, this device provides eye-level display of an angle of attack indicator. They’re becoming increasingly popular in general aviation airplanes and provides an additional sense of angle of attack, especially during low speed maneuvers.
You can see a similar STC part here
https://sarasotaavionics.com/avionics/valkyrie-hud-kit

Oh my god the product in the link! Talk about confusing and counterintuitive symbology!!!

I’m not sure why you would call it confusing per se. It displays the same info as any other angle of attack indicator.

@Jpe61 "counterintuitive" ? Could you elaborate on what you mean exactly?

Thanks for answer. Do you have some insight on what sensor this uses? Because airliners AOA use some specific sensor, while this one doesnt seem to need this.

Wedges, triagles, a split ball, a line. Designers of this system forgot the KISS principle.  I have a hunch I've seen this symbology in a military HUD somewhere, not sure. If it in fact is copied from a military system, it is still unnecessarily complicated.

Let me add: a very good addon in principle, I just think that in a high load situation quickly reading that correctly might prove difficult.

@Jpe61 Other than the see-thru nature of it, this looks very much like the AoA indexer I remember from the T-38. Having flown with it for a while, it became quite familiar and intuitive to refer to in flight.

@Jpe61 Don't confuse violation of the KISS principle with your own lack of familiarity with the indications. It is a quite simple and intuitive display, inherited from military aircraft, when you have become acquainted with it. Most instruments in aircraft, even the best designed modern ones, can look counterintuitive to those unfamiliar.

If you think you can devise a simpler system than that used in actual production, and which sufficient professionals and experts would agree is simpler, you better get manufacturing fast because I don't think those experts and professionals will all be waiting for someone else to make it first.

The world is full of examples of solutions deemend simple, superior and whatnot by professionals and experts, which in actual use have proven to be confusing, even to fatal extents. Engineers at Nokia were convinced Symbian was the best and most intuitive UI. No, it was not.

@Jpe61 You are seeing the indicator with all of its sections illuminated. Many displays will form weird shapes and show confusing indications when all the sections are illuminated. In use, combinations of those segments are illuminated to produce things like colored arrows, a line, or a circle.

Just for the record, I was not assuming it looks like that all the time

This is an Angle Of Attack indicator, specifically Alpha Systems’ Eagle Above Dash HUD Kit:

Thanks for that link! The operation and installation manuals give a good explanation on the principles (measuring the air pressure difference on two nearby locations, from what I understood).

Appropriate that they're mounted next to a little eagle statuette...


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Why does this plane have vapor trails coming out of wings?
See this video of Birmingham strong crosswinds landings:

At 2.57, there is a 737-800 landing (screen shot below).
One can clearly see some vapor (?) coming out of what seems to be two holes on both wings, from 3.03 to 3.10, were the plane lands.
This does not seems to be a 'classical" vapor trail, as asked in this question, as it clearly does not occur at the tip of the wing.

What is this? What explains this? Something specific to the 737-800?
Edit: While it is clear to me that this is a vapor trail, the question is more about why there is a vapor trail at this precise location of
the wing.
Usually, these appear at the wing tip, and this is clearly not the case
here. Maybe something with the flaps, as suggested ?
Thus, while the question itself is not exactly a dupe, this answer (and the associated pictures) give a clear explanation.

It may be the vortices created by the flap tips just as it happens with the wing-tips

@ppinto Mmh, could be, indeed. But why only the 737 ? Some specific flaps geometry on that plane?

@RonBeyer Thanks for suggestion, but not a dupe, IMHO. My question is more about why there is a vortex/vapor trail at that precise location of the wing (usually, they appear at wing tip).

@kebs IMHO that is explained in Peter Kämpf's answer to the other question. The last photo in there shows exactly this phenomenon. What exactly is unclear?

Oh, indeed. The linked question is not a dupe as itself but the answer you mention does indeed answer my question!

This are indeed the vortices a wing sheds where lift suddenly drops. That they occur at mid-span and not at the tips is due to flap deflection. They do indeed start at the outer edge of the Fowler flaps. @NilsNielsen explains well why you see a white line at the core of the vortex.
See this photo (source): This is the same thing happening. It is not specific to the 737-800, but to any aircraft with powerful flaps which end at mid-span to make space for the ailerons.

Great answer, thanks.

Those are tip vortices, which are propagated into the plane's wake from sharp corners and projecting tips along the trailing edge of the wing like the corners of the flaps (when extended) and the ailerons. You can imagine them as "sideways tornadoes"; much has been written about them and I recommend you search this site for more info.
The reason they appear as white vapor is that the pressure inside the vortex is lower than that surrounding it, and if temperature and humidity conditions are just right then the pressure and temperature drop inside the vortex will push water vapor out of solution and make the otherwise invisible vortex easy to see as a wiggling "rope" of water droplets.

Ok, so if I get your point, this is just some optical illusion: they are generated at the wing tips but appear on the middle of the wing due to view angle ? Is that it ?

no, they originate at the outboard corners of the trailing edges of the flaps. In your original image, the flaps were not directly visible.


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Calibrating Cessna 172R fuel tanks
I am replacing our fuel sender units with new ones from CiES and need to calibrate how much fuel each tank can hold.  Each tank has a capacity of 28 gallons but only 26.5 gallons is usable.  The question is: Where do I drain the tank so I have a good "empty tank" to start from?  Do I just drain from the 5 wing sumps until they are dry?  Will this leave the 1.5 gallons of unusable fuel in the various nooks and crannies of the tank?  With an empty tank I should be able to add 26.5 gallons to fill it to the top.  But I need to set the starting point on my Aerospace Logic fuel gauge to either 0 gallons or 1.5 gallons.  Any advice on how to do this calibration properly?

You need to calibrate the sensors to what the engine considers empty, so empty for the purpose of the fuel gauge indication means the gauge must read empty with the unusable fuel in the tank (a savvy pilot who is in a fuel emergency, and is about to run dry, can get access to some of that unusable fuel by skidding, especially if the tank is long spanwise).
What I did when calibrating the dipstick I use to measure fuel quantity in my own airplane during preflight is drain the tanks via the gascolator so that unusable fuel remains in the tank.
So either do that, or deduct the published 1.5 gal unusable fuel from the measurement if you empty the tank by the tank's sump drain, which is supposed to remove everything. Make sure the wings are level.

Draining the fuel from the gascolator makes the most sense to me too.  That assumes there's 1.5 gallons X 2 tanks of unusable fuel somewhere in the fuel system.  That also means I should be able to 26.5 gallons to each tank to reach a "full" level reading on the fuel gauge.  I am starting at 1.5 gallons unusable on my gauge so between the usable and unusable fuel the gauge should read 28 gallons when I'm done.  I'll see what happens.

An A&P/IA I consulted said to just drain the tank from the lowest sump drain (our Cessna 172R has 5 drains per tank), add 1 1/2 gallons to represent unusable fuel and then add the 26 1/2 gallons of usable fuel for a total tank capacity of 28 gallons.  But I am coming up two gallons shy of this before the tank is full.  Maybe the 1 1/2 gallons of residual unusable fuel is already in the tank somewhere so I didn't need to add it myself?
All the Cessna procedures really don't address what an empty tank is once it has held fuel in it's lifetime.  Adding 1 1/2 gallons to a brand new empty tank could make sense.  But adding it to a tank that has held fuel and been drained may not.
Has anyone else tackled this problem before?

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.


text:
Can the autopilot (or stall avoidance system?) of the B737 MAX 8 be overridden by sheer force?
A New York Times article from today about the Lion Air Flight 610 crash claims that in order to control the airplane the pilot

could have braced his feet on the dashboard and yanked the yoke, or control wheel, back with all his strength.

Thanks to T.J. Crowder's comment I realize there is not only the autopilot but also a (new?) stall avoidance system installed on this new line of B737s.
Is it true that either one can be overridden by a simple application of sufficient force to the yoke? If so:

What is the respective underlying mechanism for the systems?
What force would be necessary, respectively?
Are both systems designed such that they can be overridden simply by applying an unusually strong force, or would that be just a violent and "unofficial" way to control the yoke despite the systems' best efforts?1

I understand that the main flight controls of this recent incarnation of the Boeing 737, the MAX 8, are still hydraulic. Does that play a role in the "override by sheer force" possibility?

1
A design which would allow a pilot to eventually control the plane just by applying excessive and unusual force (as opposed to perform a complicated series of button presses and/or touch screen actions to disable either system) would in my opinion make a lot of sense as a "panic mode".

It's not clear from that article that it was the autopilot that the captain would have had to overcome. It's a "system" on the MAX 8 designed to kick in automatically to correct a stall. The speculation is that it got bad data and "corrected." I think we can safely assume that if the plane had been on autopilot and suddenly pitched nose-down, the pilot would have pulled back on the yoke with more than the force required to disengage the autopilot. Based on Boeing's guidance (kill power to tail stabilizers), the "system" isn't the autopilot, but smth else -- and apparently harder to overcome.

@T.J.Crowder Oh, that is an interesting point. Thanks.

The system in question only applies when the autopilot is NOT engaged.

I asked a very similar question about the Airbus varient relating to the Hudson River incident

Most transport category aircraft, including B737, have the elevator, the main surface controlling pitch, attached to a horizontal stabilizer that is also movable.
The elevator is controlled using the control column (yoke), while the stabilizer is moved using the trim wheels on the central console.
This arrangement means the command from the elevator is added to the command from the trim. So when the trim is all the way pitch down, the maximum pitch up command the elevator can provide before it hits its mechanical limit is severely limited.
Autopilot: Yes, but…
The autopilot moves the elevator instead of the pilot, and in B737 the yokes actually move as it does so. So the pilots can pull on the yokes to override it. As already mentioned in another answer, the autopilot is limited to force of 25 lbs, so even if it does not disconnect when the pilots apply 21 lbs as designed, they should be able to overpower it—and 25 lbs should not need one to brace too hard anyway.
However, the autopilot also actuates the trim occasionally to transfer the needed pitch command from the elevator to the stabilizer. This reduces drag a bit by eliminating the angle between the stabilizer and elevator, and it means the aircraft will continue to fly straight when the pilots disengage the autopilot.
But it also means the aircraft will be trimmed in whatever way the autopilot left it. If that means it is trimmed far in one way, the pilots ability to give the opposite command with the elevators alone is limited and they need to move the trim too.
MCAS: No
The Maneuvering Characteristics Augmentation System, however, works differently. It does not do anything at all with the elevators and simply adds nose-down trim. If it malfunctions, it will move the stabilizer all the way to the mechanical stop, and in this trim position, the elevator does not have enough authority to keep the nose up at slower speeds.
The yoke will hit mechanical stops at large, but still reasonable force (IIRC 40 or 50 lbs). All the hydraulic cylinders will be at their mechanical limits as well, so applying more force won't help. The elevator can't go any further. The only remedy is to turn off the electric trim—which is used by the MCAS, and by trim switches on the yoke—and adjust the trim using the trim wheels.

This is in line with what I have read in the meantime, and makes complete sense. It appears to contradict the Times article though ("with all his strength"). It's well possible that that statement was wrong because of an incomplete understanding of the technical situation at the time of its writing. Although 25 lbs (the weight of a large bucket of water) horizontal force are significant, and one may wish to push against something to sustain it, I'm not sure it qualifies as "with all strength".

The relevant points here are that (1) the yoke force is not directly translating to hydraulic pressure but instead controls valves which have hard technical limits (all open, all closed); and (2) that the elevators also have a hard technical limit which is not sufficient to compensate for an all-out mis-trim of the horizontal stabilizers. Both make it impossible to compensate an all-out wrong trim through yoke forces.

@PeterA.Schneider, indeed, this is not the first accident where inability compensate for incorrect trim with elevators was important contributing factor. Aeroflot flight 141 and XL Airways Germany flight 888T come to my mind. In the first, there is no official conclusion, but incorrect manipulation with trim is considered to be a likely cause, in the later the fact the aircraft was trimmed nose high (and autotrim went offline) from the slow flight made the stall recovery harder.

"25 lbs should need one to brace too hard anyway." Did you mean "should NOT need"?

@mike, thanks, corrected.

I'm not sure of the full story here, but if you pull the controls of a 737 while the autopilot is engaged the autopilot will trip and the pilots can fly the plane manually. This requires about 25 lbs of force.
There is also a button on the yoke where you can disengage the AP. So if the AP was controlling the plane and going into a violent descent the pilots should have been able to cancel it by pulling the yoke or pushing the button on the yoke or the mode control panel below the windshield.
And no, the controls being hydraulic doesn't play a role in the "override by sheer force" possibility.
Edit:

The autopilot servos are limited to 25 lb of force for single channel operation. Separate force sensors measure pilot column input and the autopilot will disconnect if the force applied by the pilot(s) exceeds 21 lbs.

Source

Why would the override be only triggered on such high stick forces? 25 lbs sounds like a decent amount of force.

I'm not sure why they constructed the plane this way. But my guess is that the underlying cause is margin for error without disconnecting the AP. 21-25 lbs of force is not really that much especially not in an emergency, just give the yoke a solid "pull" and it'll be enough. Keep in mind it's force and not pressure

@curious_cat I would assume that it's a safety requirement that disengaging the autopilot requires a conscious act by the pilots. 21 lbs of force are probably high enough to not be exerted accidentally but still low enough to be produced ad hoc. (21 lbs seem to contradict the "feet on the dashboard" bit in the article. OK, maybe one needs a bit of pushing against the dashboard because it's a horizontal force.)

Thank you for the answer. Can you give us the source of your quote?

Hi, the data i quoted can be read here: http://www.b737.org.uk/incident_ei-ebw.htm

Just to give a reference point for how much strength it takes to overcome the autopilot, the spark plugs on my Cherokee take 30-35 foot-pounds of torque. It takes no effort on my part to tighten them.

@curious_cat To avoid accidental a/p disconnect. Even with this requirement, there have still been a couple of crashes caused by inadvertently disconnecting the a/p by knocking against the yoke, so some aircraft don't let you disconnect the autopilot this way.

@curious_cat Aeroflot 593, Eastern 401. Opposite failure to disconnect would be China Airlines 140.

@JScarry , Force=/=Torque

I read an analysis somewhere claiming that on the accident flight, FO control force exceeded the disconnect limit, and that the system then with single channel only controlled one elevator (no pitch input on CPT control column) which was not sufficient to counter nose up stabiliser.

@PeterA.Schneider, note that this answer is completely irrelevant, because that system is not autopilot. That system is a separate system that manipulates trim on its own. Trim is not controlled by the control column, but by the trim wheels on the central console, so it cannot be overpowered by pulling on the control column, and because the trim has larger range of authority than the elevator, pulling on the yoke can't compensate for too bad trim.

Out of trim is no way to fly
The issue with the B737MAX as detailed in the Emergency Airworthiness Directive from Nov. 7, 2018 is not that the plane is applying a nose-down elevator input through the autopilot servos — this would be trivial for the pilots to overcome, even if the servos failed to declutch when the pilots pulled the yoke.  The problem is that the aircraft may be applying a repetitive, nose-down pitch trim input to the stabilizer trim system (essentially, an autotrim command), and to quote our very own Capt. Casey Webster, "an out of trim transport category airplane can be a beast to fly".
In other words, an out-of-trim situation in a transport category aircraft can lead to quite high control forces, hence the reference you saw about the pilot bracing their feet on the instrument panel and pulling with all their might to overcome the grossly nose-down stabilizer trim.  (Of course, you'd want the other pilot to cut out the trim motors while holding onto the trim wheel with a free hand to keep the trim situation from getting worse.)

Speculating about accidents that are under investigation is off-topic on this site. That's why the question has been updated to be about aircraft systems in general. Please [edit] your answer to match the question, or you can choose to delete it if you don't have anything to say about the question.

I edited the answer to remove the reference to JT610. This answer is valuable since it addresses and clarifies the core issue (thus improving my own muddled understanding).

It's worse, really. The stabilizer (trim) and elevator commands are additive, so nose-down trim reduces the maximum nose-up command that can be given.

With typical hydraulic controls, the mechanical control cable circuit just operates control valves on the hydraulic actuators.  The control valves normally only have fairly light centering springs that take only a few pounds of force to overcome. With no other devices in the control circuit, you could move the control column with your pinky finger.
Control feedback forces come from pitch feel devices in the control circuit that use internal spring packs (bungees) and/or roller cam devices to provide a variable resistive force. But the feel units won't drive the circuit, only provide resistance.  Two devices can drive the elevator circuit in theory; the autopilot servo and the stick pusher (which is like an autopilot servo that only operates one way).
Autopilot and stick pusher servos have two clutches, a meshing teeth on/off clutch, and a friction slip override clutch.  If the A/P servo runs away for some reason, and you can't trigger a disconnect electrically, it is possible to overpower the slip clutch in the servo, but it is like the stick is in not-quite-solidified concrete the whole time you are trying to move it.  But you can move it.
The stick pusher servo is similar, but the stick pusher is designed to drive full nose down and release almost immediately.
In any case, if you had an elevator hard over like that and the electrical disconnects (there are usually several difference switches that can perform the disconnect function), the next action would be to operate the mechanical pitch disconnect to separate the left and right elevator circuits.  You end up with one free elevator, which will give some control, at least enough to neutralize the overall input.
One possibility is the shock and surprise of the event, whatever it was, overwhelmed the crew and they didn't follow through on all the memory items for that kind of emergency.  At this point, who knows.
Also remember that media stories on these kinds of incidents are almost always wildly inaccurate.  Anyone who has worked in any kind of technical specialty and reads media reports related to their specialty knows that they are wrong most of the time.

Thanks for the details. (Btw, I have more confidence in the NYT than in most others. They pay a lot of attention to factual correctness and do publish corrections. If you think the article is factually incorrect don't hesitate to send a correction; they surely appreciate it.)

Keep in mind that the both the Boeing OMB and the FAA EAD refer to the spurious aircraft inputs as pitch trim (stabilizer) inputs, not as pitch (elevator) inputs.


text:
Which aircraft had the shortest operational life?
I read in Wikipedia that the operational life of Consolidated B-32 was limited to just a handful of months (January to August 1945).
Please note that B-32 wasn’t an experimental model, but an aircraft which was industrially produced in relatively large scale, was issued to some operative wings and was engaged in some actual combat events, showing even several appreciated features.
Was it the most short-lived aircraft type, all that considered?
I mean, is there another military aircraft type, assigned for combat mission to operative units, which was discontinued earlier than the B-32 (only seven months after the beginning of service)?

Japanese Ki-100 made its combat debut on the night of 9 March 1945. The last loss of a Ki-100 occurred on 14 August 1945, a day before the surrender of Japan. Hence the  interceptor has been in the service for 158 days, or 5 months 5 days, with 396 units produced.
Looks like nothing bad can be said about this interceptor. It has been recently developed, without major flaws, and, as such, was obviously superior to the older models. It was between the first interceptors to feature the factory-installed armor and self-sealing fuel tanks, and some think it was the best interceptor used by the Army during entire war. But, with the end of the war, it was no longer required.

Interesting case, a true candidate for the “short-timer” award in its category, I suppose.

Note that armor and self-sealing fuel tanks were only new in context of Japan—they were already common in western aircraft.

The Heinkel He-162 first saw combat in mid-April 1945 and the war ended on May 8 1945. https://en.wikipedia.org/wiki/Heinkel_He_162

That is true, but they were deployed operationally in February 1945, so I think their  "service life" could be considered a bit longer.

Another contender - the Ambrosini SAI.207 had under two months of active service.

SAI.207 model - source
Exact dates are hard to come by, but they were first deployed operationally in July 1943. Even before the armistice of 3 September all the aircraft had been returned to SAI-Ambrosini for refurbishment, so it seems certain that fewer than 60 active days in service could be claimed for the type.


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Aircraft wing stress design for 4 engine aircraft
Can anyone tell me how aircraft wings are designed for mounting the engines. My area of self study is a typical engine on the A380 weighs 8000kgs and it’s weight is forward of the wing. As the wing stays the same angle of attack no matter whether the engine is installed, under power or at idle I cannot understand why there is no turning force on the wing. With this 8000kgs weight hanging out on the outboard engine where the wing is thinnest then why does it not have a twisting effect on the wing. I can understand how the wing can be stressed to allow for when an engine is installed but if you look at the wing profile it’s unchanged whether the engine is mounted or not.

Trust me, the wing does twist. But it needs to be stiff enough so the amount of twist is small. But all torsion moments are accounted for and the wing has a different twist distribution on the ground than in flight, because the loads change. Here is some further reading.

Any load comes with deformation. Paraphrasing a professor from memory: "A large solid steel beam can only provide the force to support an ant walking on the end of the beam by bending. The only possible alternative is for the beam to break off."

I understand this but not why the wing does not twist by the overhang in front of the wing.